明清统治者推行“海禁”和“闭关锁国”政策，其主要影响有（）

①保护了民族工业发展

②失去了开拓海外市场的契机

③避免了西方殖民侵略

④妨碍中国与世界的正常往来

A.①②

B.②④

C.①③

D.②③

If being carried out successfully, the plan will completely change the traffic conditions in the city.

A．carried
B．is carried
C．having been carried
D．to carry